1. Field of the Invention
This invention relates to a dental gel containing stannous fluoride and more particularly to a process for producing a stannous fluoride gel having improved ribbon or stand-up characteristics when dispensed from a tube. These gels exhibit surprisingly good stannous ion and fluoride ion stability.
2. The Prior Art
Stannous fluoride (SnF.sub.2) has been reported to be an effective agent for treating various oral conditions. The most important dental benefit imparted by stannous fluoride is the reduction of dental caries. Stannous fluoride-containing over-the-counter dentifrices have been classified by the U.S. Food & Drug Administration as therapeutic agents that provide protection against the development of dental caries. Early stannous fluoride dentifrices contained abrasive systems that reacted with fluoride making these products ineffective in reducing tooth decay. Significant progress in the development of new abrasives has led to the development of stannous fluoride dentifrices with significantly improved fluoride ion availability. However, the antibacterial stannous ion undergoes rapid hydrolysis and oxidation in aqueous based dentifrice's resulting in essentially no available stannous ion.
Self applied topical fluoride products now exist based on 0.4% stannous fluoride but without formula excipients that interact with fluoride and stannous ions (e.g., abrasives, water, surfactants, etc.). The principal excipient of these stannous fluoride "gels" is the humectant glycerin. The prior art clearly shows the method of manufacture (e.g, mixing times, temperature, manufacturing equipment) is critical to ensure stability and availability of the fluoride and stannous ion. Indeed the process outlined in U.S. Pat. Nos. 4,418,057 and 4,533,544 for a stannous fluoride gel presents numerous challenges for the manufacturing team. It requires the preparation of several side phases consisting of precise levels of stannous fluoride and glycerin. Mixing temperatures can range up to 180.degree. C. which is not easily achieved in most plants without special equipment. Another draw back to the gel preparations described in U.S. Pat. Nos. 4,418,057 and 4,533,544 is that the gels have a semi-liquid consistency, and when dispensed on the bristles of a toothbrush, the gel immediately sinks through the bristles and runs off the brush so that only a relatively small portion of the dispensed product is retained on the toothbrush. Consequently, SnF.sub.2 suspended in the thickened anhydrous glycerin has not found wide acceptability as a home-care product due to the face that the semi-fluid gel composition can not be controllably retained on toothbrush bristles and then applied to teeth to reliably supply SnF.sub.2 for the treatment of dental carry.
It is therefore an object to the present invention to provide a processing scheme for producing a stannous fluoride gel which avoids the shortcomings of the prior art.
It is also an object of the present invention to provide a stannous fluoride gel with good ribbon stand-up qualities and surprisingly good stannous ion and fluoride ion stability.
These and other objects will be made clear from the following: